Turning tools and milling tools are provided with one or a plurality of indexable inserts. As shown in FIG. 1, such an indexable insert 1 includes a rake face 2 that is located on the side at which a chip 6 of a workpiece 5 is lifted up during cutting and a flank face 3 that rake faces the workpiece itself. The rake face 2 is connected to the flank face 3 with a cutting edge 4 therebetween, and the cutting edge 4 acts as a main point of action for cutting the workpiece 5.
In such an indexable insert, when the tool life expires, the edge must be replaced. In the case of an insert that has only one cutting edge, the insert itself must be replaced. However, in the case of an indexable insert that has a plurality of cutting edges, by turning the cutting insert several times on the same bearing surface, i.e., by placing an unused cutting edge at the cutting position, a different cutting edge may be used. In some cases, the cutting edge may be refixed on another bearing surface and an unused cutting edge may be used thereon.
However, in cutting worksites, there are often cases where an indexable insert is replaced or turned even though a cutting edge thereof has not yet been used. The reason for this is that when the cutting insert is replaced or the cutting edge is turned, it is not recognized whether the cutting edge has been used or has not yet been used. Consequently, it is necessary to perform such an operation after thoroughly checking whether the cutting edge has been used or has not yet been used.
As the method for easily identifying used cutting edges, an indexable insert has been proposed in which a flank face and a rake face have different colors (Japanese Unexamined Patent Application Publication No. 2002-144108 (Patent Reference 1)). Specifically, in this indexable insert, a wear-resistant base layer referred to as a wear-reducing coating is disposed on a body, and a wear-indicating layer composed of a material susceptible to wear is disposed on a flank face.
However, although the indexable insert having the structure described above has an alerting function to indicate whether or not the cutting edge has been used, the material constituting the wear-indicating layer disposed on the flank face is easily welded on the workpiece, and thus the material constituting the wear-indicating layer may be welded on the surface of the workpiece, or the workpiece material may be welded on the wear-indicating layer to cause an irregular edge, and cutting may be performed with the irregular edge. As a result, the appearance and surface smoothness of the workpiece after cutting may be impaired.
Furthermore, as in the case described above, in an indexable insert in which a wear-indicating layer is provided on a flank face, when the cutting insert is placed in a storage case or placed on a working table in the vicinity of a machine tool, it is not easy to identify which cutting edge has been used, which is disadvantageous. The reason for this is that since the flank face usually has a smaller area than the rake face, the cutting insert is often placed with the rake face up in a storage case, and also placed with the rake face up on a working table. As a result, the flank face is in a position difficult to observe visually.
Patent Reference 1: Japanese Unexamined Patent Application Publication No. 2002-144108